a new scale-up method based on the effect of ventilation on aerated fermentation systems was developed. the volatilization rate constant (kv) of a volatile compound was proposed as an index for showing quantitatively the effect of ventilation on aerated fermentation systems. the kv value of a volatile compound, 2-octanol, an inhibitor of cell growth, in a jar fermentor was affected mainly by the air flow rate and to an extent by the agitation speed. in a scale-up of culture systems having a volatile growth inhibitor as a rate-limiting factor, the need to consider both the oxygen transfer rate and the ventilation effect was demonstrated in a simple yeast model culture containing 2-octanol. it was shown quantitatively that an erlenmeyer flask with a cotton plug had essentially no ventilation effect when compared to a jar fermentor. an aerated-flask having a forced-air system was therefore designed and a new method of scale-up from this flask to jar fermentor on the basis of the kv value was proposed. the usefulness of both the aerated-flask and this new scale-up method was demonstrated with the model yeast culture (author abstract) 10 refs